1. Field of the Invention
The present invention relates generally to the marking of mold inserts to produce marked contact lenses, and more particularly pertains to electric discharge machining of mold inserts for contact lenses. The present invention is efficient, controllable, repeatable, and provides a readily visible mark in the final lens product without adding significantly to the expense of manufacture thereof.
The present invention relates to a method of imparting visible marks to stabilized soft molded (SSM) hydrogel contact lenses. Such visible marks are used as inversion indicators, which are visible marks of a special design placed on the lens to allow the user to determine if the lens is in the proper configuration or to determine if it has been inverted so as to be inside out. Other visible marks can be employed as trademarks to identify the manufacturer. Visible marks are also required in those types of contact lenses which require orientation with respect to the eye for insertion. Visible marks are also desirable to allow a user to more easily see and locate the lens when it is in a solution, such as a saline solution used in the original packaging of the contact lens or in a storage container.
2. Discussion of the Prior Art
The prior art discloses many technical approaches for solving the problem of imparting visible marks to contact lenses. Laser etching or burning is taught by EP 291459 and JP 61223820. Diamond point engraving is disclosed in DE 3316730. Printing techniques, some of which use photosensitive materials which are subjected to UV energy, are shown in GB 200614, DE 3219890 and JP 61211382, among others. Other coloring or dying techniques are disclosed in JP 62186221, JP 62186222, JP 62250286, among others.
All of these prior art approaches are slow and difficult to control, and typically add expense to the manufacturing of the contact lenses.